1891.] The Hat Creek Bad Lands. 969 
First and most abundant were the Oreodons and their allies. 
The number of their remains shows that they most probably 
formed large herds. Rarer were the horse-like forms, which, how- 
ever, resembled but little the horses of to-day. Then there 
were camels and rhinoceroses, and largest of all the immense 
Menodus, the lower jaw of which measured about two feet in 
length. These animals fed on the vegetation, while the cats 
and Hyzenodons of the time preyed on these. How the bodies 
were transferred to the place where we find the bones is a prob- 
lem easily solved. Probably there were freshets caused by abun- 
dant rains, and numbers of animals were swept by the stream 
into the lake. Here the bodies floated about, disturbed by the 
gases of decomposition, until a part dropped here and another 
there. This explainsethe scattered condition of the bones to-day. 
Even in the solid rock it is unusual to find more than two or 
three bones together. Certain it is that these animals were not 
mixed where we find them. 
At length the conditions changed. The lake still remained, 
gathering sediment at the bottom, but the mammalian remains 
are much scarcer than before, and even in the upper portions of 
these bad-land strata they are much less abundant than in the 
lower beds. What was the cause? I do not know. ,, Still the 
lake continued laying down stratum after stratum until there was 
at least more than a thousand feet of rock piled upon the top of 
the fossils. How much more there was we do not know. The 
Buttes are our sole register in this respect. We no not know 
how much erosion there has been from their tops. 
At last the lake became dry, and its old bottom was exposed 
to the air, and now erosion began. Looking across the Bad 
Lands from the tops of the Buttes, and seeing that valley forty or 
fifty miles across, and with an average depth of eight hundred or 
a thousand feet, one no longer wonders at the muddy Missouri 
or at the immense alluvial deposits which the Mississippi has 
made; and yet this same erosion is going on and has been going 
on ata thousand other places of equal extent. 
Rapid erosién now ceased, and the broad valley with its gently 
undulating surface gained a soil. Then a second erosion began, 
and it is this second erosion which has produced the Bad Lands. 
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